const btn = document.getElementById("btn");
const boxes = document.getElementById("boxes");

btn.addEventListener("click", () => {
  boxes.classList.toggle("big");
});

for (let i = 0; i < 4; i++) {
  for (let j = 0; j < 4; j++) {
    let div = document.createElement("div");
    div.style.backgroundPosition = `-${j * 125}px -${i * 125}px`;
    div.classList.add("box");
    boxes.appendChild(div);
  }
}
